One of the functions of the solid-state image pickup device of recent interest is the electronic shutter. The electronic shutter function makes possible the acquisition of a precise image of an object which is moving at high speed by dumping electrical charge accumulated within the device once during a vertical blanking period and subsequently receiving light again until the normal read time.
On the other hand, a device consisting of photoelectric transducer elements arranged in matrix form, vertical transfer routes, horizontal transfer routes, and a transfer control part is well known as a solid-state image pickup device. Such an image pickup device may be constructed as, for example, an interline transfer type CCD. In that case, the vertical and horizontal transfer routes consist of shift registers which supply transfer pulses to the CCD transfer electrodes.
Construction of a high speed shutter by adding the electronic shutter function to an interline transfer type image pickup device yields poor results. The quantity of signal photoelectrically converted is small in comparison to the smear quantity generated in the device, owing to the extremely short exposure time of the high-speed shutter. As a result, obtaining an image of practical utility is not possible.
Furthermore, another difficulty exists. Although the conventional interline transfer type device can accumulate signal charged in a frame and can read a frame image in the interlace mode, it is well known that adding the electronic shutter function to such a device makes reading the frame image impossible. That is, when reading a frame image in the interlace mode with the conventional device, the photoelectric transducer elements assigned to a B field are receiving light and accumulating electrical charges without interruption even during the period in which an A field signal is transferred to and within the vertical CCD. In this way, the photoelectric transducer elements are continually performing photoelectric conversion and charge accumulation except while electrical charges are transferred to the vertical CCD. Therefore, if a specific exposure period is introduced into a system where the electronic shutter function is added to an interline type image pickup device reading signals in the interlace mode, a slippage of 1/60 second occurs between an A field image and a B field image. Thus, as the shutter time is diminished for a moving object, a desirable frame image cannot be obtained. In other words, when the electronic shutter function is added to the interline type CCD image pickup device, the frame image cannot be read. As a result, when a solid-state image pickup device supplemented by the electronic shutter function is applied to an electronic still camera, only a field image can be obtained, yielding the particular disadvantage of a reduction in the resolution.
It should be mentioned that the frame interline type (FIT) CCD is known to reduce smears by transferring the signal charges at high speed in the vertical direction, thus enabling a high speed shutter operation. However, the disadvantage of the device is that it requires a charge accumulating part in addition to the light receiving part, resulting in an increased chip area. Further, even with the FIT type device, a frame image cannot be obtained in the electronic shutter mode.